Wear resistant electric contact



can... 1.... 16,1940 1 1 2,137,32

UNITED STATES PATENT OFFICE WEAR RESISTANT El'JECTRIG CONTACT Franz R. Hansel, Indianapolis, Ind., assignor to P. R. Mallory & Co. Inc., Indianapolis, Ind., a corporation of Delaware No Drawing. Application September 25, 1937,

Serial No. 165,767

a 3 Claims. (Cl. 200-166) This invention relates to electrical make-andwear resistance of electrical contacts; consists break contacts. in a quenching operation of the silver base alloy An object of the invention is to provide an elecof suitable composition. The temperature from. trical make-and-break contact. which the alloys are being quenched, usually 'Another object of the invention is to improve ranges from 500degrees C. to just below their 5, the characteristics of electric contact elements melting points, or critical points at which one containing silver. phase becomes liquid. After this operation, the

A further object of the invention is the provicontact materials are very soft and usually show sion of an electrical make-and-break contact a minus reading on the Rockwell B scale. The

30 having high wear qualities being produced by second operation in my preferred heat treatment in means of a special heat treatment. consists in a drawing at a temperature which is Other objects of the invention will be apparent usually below 500 degrees C. In some cases a from the following description taken in conneotemperature as low as 200 degrees C. may be used. tion with the appended claims. In general, it can be stated that I can vary the w The presentinvention comprises the combitemperature range at which aging proceeds, in! nation of elements, methods of manufacture, and as long as I vary also the time of aging. Usually the product thereof brought out and exemplified at the higher temperature, a shorter time is rein the disclosure hereinafter set forth, the scope quired to produce the desired results. of the invention being indicated in the appended The copper-silver alloy, general known as coin 20 claims. silver, containing approximately 10% copper and mi While a preferred embodiment oi. the inven-e the balance silver can be heat treated, for iii--- tion is described herein, it is contemplated that stance, by quenching from approximately 750 considerable variation may be made in the methdegrees C. and subsequently aging at 250-300 dead or procedure and the combination of elements grees C. The resulting Rockwell B hardness at as without departing from the spirit of the inventer such treatment will be 75 Rockwell B or betmy tion. ter. In addition, the material can also be cold For many purposes, it has heretofore been cusworked and the hardness still further increased. tomary to use silver alloys which have desirable I have also found that contact materials which. electrical characteristics, such as low contact reare susceptible to such heat treatment will have so sistance. While such contacts have been found an improved electrical conductivity after heat at fairly satisfactory, they always had the disad treating. Usually the electrical conductivity is vantage that they are soft and therefore are higher, the less material is in solid solution with easily deformed or wear down quickly in service. the silver. The precipitation treatment, which My invention provides a means to overcome this is applied to the contacts in the above described 35 disadvantage and produce a wear resistant silver manner, causes the solid solution formed during base contact material. I quenching, to disintegrate and precipitate an- My invention consists in using a silver base 9.1- other phase. loy, containing certain ingredients which have a I can regulate the precipitation in such a manlimited solid solubility in the silver. Furthernor that the precipitated particles are not visible 4 more, the solid solubility will change as a func-- under the microscope, but are very finely and m tion oi the temperature. I have found that e'lecsub-microscopically distributed. Such a very trical contactmaterials of such a structure can fine and almost homogeneous structure has been. be subjected to a simple heat treatment, after proven to be ideally suited for electrical contact which the wear resistance is greatly improved. purposes. Usually, the best results are obtained a Itls known to use alloys consisting of silver and in electrical contacts which have only one phase, M copper for electrical contacts. The alloys were present. If another phase is located, for in usually made up in the conventional manner by stance, in the grain boundaries, in the form of melting together the ingredients and then Iorglarge particles, such locations will be attacked lng some down to a size which would allow to during the contact performance and such 5 either roll the metal into sheet or draw it into phenomenon as material transfer will start from wire. I havefound that I can take alloys prethese heterogeneous areas. Material transfer pared in the above described manner, and procan become a very serious obstacle in contact duce an increaseinhardness heretofore unknown performance and in many cases will determine for electrical contact purposes. the life or a contact. Hy producing the hetero My preferred heat treatment for improving the geneous phases in such a finely distributed manner, with the above described heat treatment, I have found that these difficulties can be entirely overcome, and that materials of this nature act as quasi homogeneous.

I have found that to binary silver copper alloys, also additional metals may be added, without adversely affecting these hardening char-' acteristics. A metal which I havein mind particularly, is cadmium, because the latter produces rather desirable contact resistance characteristics in silver base alloys. It is possible to have as much as 16+20% cadmium present and still be able to age harden the silver base alloys. It has been found possible in electrical contact alloys to replace cadmium, either partially or totally, by zinc, and stillobtain satisfactory contact performance. In silver alloys of this nature, it is also possible to have up to 5% present of a metal of the iron group or of manganese;

Instead of using pure copper as an age hardening ingredient for silver base electrical contacts, I have found that also intermetallic compounds can be used and I have found that a copper aluminide in silver will produce very effective hardening. With 3% copper aluminide, the hardness can be improved from a minus Rockwell B reading to more than 80 Rockwell B. I have also found that I can substitute forthe aluminum one of the elements magnesium, antimony, silicon, palladium, zirconium, titanium, beryllium or chromium.

Since it is possible to vary the elements which are added to the silver base to produce increased hardness by the presence of a highly dispersed phase in a quasi-homogeneous matrix, I do'not limit myself to the specific percentages in this disclosure, but use them as illustrative of proportions only and not as limiting proportions.

It is preferred that the dispersed phase be submicroscopic in nature and uniformly distributed throughout the matrix of the silver material so that the resulting composition might be described, as being on the borderline between a solid solution and a heterogeneous mixture, which I describe as a quasi-homogeneous composition.

The electric contact of the present invention can be fabricated into various forms depending upon the uses for which theyare required; The contacts may be used whereas silver contacts have been used in the art, as, for example, for

- relay contact purposes.

While the present invention as to its objects has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the appended claims. v

What is claimed is:

1. An age-hardened electric make-and-break contact formed of silver containing copper in amounts not exceeding the solid solubility limits at Q C. but exceeding the solid solubility limits at 250 C., said'contact being characterized by a quasi-homogeneous physical condition wherein there ispresent a sub-microscopic precipitated phase uniformly distributed and highly dispersed in the silver matrix, said phase consisting pre-' FRANZ R. HENSEL. 

